1. Field of the Invention
The present invention relates to a color diffusion transfer photographic material and, more particularly, to a silver halide color diffusion transfer photographic material capable of providing images having less stain.
2. Description of the Prior Art
Various systems for the color diffusion transfer photographic process are known. For example, a process using dye developers as described in U.S. Pat. No. 2,983,606, a process using diffusible dyes produced by a reaction between a color former and an oxidation product as described in U.S. Pat. Nos. 3,227,550 and 3,227,551, and a process described in U.S. Pat. No. 3,628,952 or Japanese Patent Publication No. 10,240/59 are known. These processes possess in common the features that a dye image-providing material-containing silver halide emulsion layer and an image-receiving layer are used in combination, and that the silver halide emulsion layer is processed, after exposure, with an alkaline processing composition having a high ph to transfer diffusible dyes to the image-receiving element. These photographic film units are designed so that the light-sensitive element is exposed using a self-processing camera and is then passed between a pair of pressure-applying members contained in the camera (for example, a pair of rollers or a slit having a structure capable of applying pressure) to thereby spread a processing solution on the exposed light-sensitive element and rapidly process the light-sensitive element, thus rapidly obtaining color positive images in the image-receiving element.
Since these film units require rapidity and handiness, the transferred images are not usually washed with water. Also, with film units comprising the image-receiving element and the light-sensitive layer which is not to be separated from the image-receiving element after transferring images, it is impossible to wash the transferred images with water. Therefore, stains result in the high light areas of the transferred images during storage or the transferred image colors darken deteriorating the photographic quality.
More specifically, for example, in the color diffusion transfer photographic process using dye developers, the spread processing composition permeates into an exposed light-sensitive element containing at least one silver halide emulsion initiating development and, as a result of the action thereof, the dye developers are oxidized and are immobilized in the developer areas.
This immobilization clearly depends in part upon the mobility or solubility of the oxidation product of the dye developers being less than that of the unoxidized dye developers. This immobilization is considered to also depend in part upon a localized reduction of the alkali concentration which is a function of development.
Since unreacted dye developers in the undeveloped areas of the emulsion are diffusible, an imagewise distribution of the diffusible unoxidized dye developers is formed as a function of the exposure and development of the silver halide emulsion. This imagewise distribution of the diffusible unoxidized dye developers is transferred, at least in part, to a superposed image-receiving element. In this transfer process, oxidized dye developers which are less mobile are clearly discriminated from unoxidized dye developers, and transferred images are formed on the image-receiving element as an image.
When an element containing silver halide emulsion layers with different light sensitivities, each emulsion layer being associated with a dye developer which is in a substantially complementary relation with the main light-sensitive regions of the emulsion, that is, when a red light-sensitive silver halide emulsion, a green-light-sensitive silver halide emulsion and a blue light-sensitive silver halide emulsion are associated, respectively, with a cyan dye developer, a magenta dye developer and a yellow dye developer, each dye developer is oxidized, upon processing the light-sensitive element containing these elements with a processing composition, in the exposed areas of the associated emulsion and becomes immobilized. The remaining dye developers in the unexposed areas are diffused and are transferred to the image-receiving material.
Therefore, when a large amount of unoxidized dye developers are distributed in the sufficiently exposed negative areas corresponding to the high light areas of a photographed object, the dye developers diffuse into the image-receiving material similarly with the unexposed dye developers present in the unexposed negative areas corresponding to the dark areas of the photographed object, resulting in indistinct transferred images having a high minimum density.
Even when used at a comparatively strong alkalinity of a pH of about 13, typical dye developers function as a weak silver halide developing agent. Therefore, when these dye developers are used, the expected maximum density, gradation and sensitivity cannot be obtained. Since immobilization of the dye developers is a function of the emulsion developing agent, the transferred images obtained in this process exhibit an undesirably high minimum density, a low maximum density and a low contrast in the high light areas. These results may be attributed in part to factors such as the developing activity of the dye developers as a silver halide-developing agent is weak, and that all of the dye developers surrounding the silver halide are not effectively utilized. In order to remove these defects, the use of auxiliary silver halide-developing agents such as 4'-methylphenylhydroquinone (e.g., as described in U.S. Pat. No. 3,039,869) and of development accelerators such as N-benzyl-.alpha.-picolinium bromide (e.g., as described in U.S. Pat. No. 3,173,786) has been suggested. However, the use of such compounds entails the disadvantage that the density in the high light areas of the transferred images is high, even though the undesirable high minimum density, the low maximum density and the low contrast of transferred images are removed to some extent. This defect is particularly serious with film units in which the image-receiving element need not be separated from the light-sensitive element after the completion of the image transfer.
That is, the density of the high light areas of the transferred images greatly influences the visual impression received, even when the density is small. The smaller is the absolute value of the density, the better. Also, the blue density is desirably not higher than the green density and the red density. The high light area of the images providing a high blue density causes the disadvantage of a yellowing phenomenon which is unattractive to image viewers.
Furthermore, the defect has been found that the colors of the transferred images formed by transferring part of the dye developers such as red, green, blue, yellow, magenta, cyan, etc. darken during storage with the lapse of time. This color darkening varies depending upon the conditions of storage. This is particularly serious with film units of the type in which the image-receiving element is to be separated from the light-sensitive element. Such undesirable density in high light areas and undesirable density resulting in the darkening of colors are called stain.
Where dye image-providing materials other than the above-described dye developers, such as are described in U.S. Pat. No. 3,443,441, German Patent Application OLS 2,230,014, U.S. Pat. Nos. 3,725,062, 3,728,113, Japanese Pat. No. (OPI) No. 33826/73, Japanese Patent Publication No. 32191/73, U.S. Pat. No. 3,245,789, German Patent Application OLS No. 1,930,215, U.S. Pat. No. 3,443,940 and the like are used, similar stain occurs in the transferred images as long as the auxiliary silver halide-developing agent (U.S. Pat. No. 3,039,869) such as the above-described 4'-methylphenylhydroquinone is used in combination.